Aqueous paint systems based on water-dilutable or water-soluble stoving binders have the advantage that they contain only small quantities of organic solvents which are lost during hardening and which pollute the environment or necessitate expensive absorption or incineration plants. The solubility of these binders in water is generally attributable to the presence of chemically incorporated, amine-neutralized acid groups, particularly carboxyl groups, or chemically incorporated acid-neutralized tertiary amino groups (cf. for example DE-OS 2749691, EP-A-218 906 or L. Dulog, Die Angew. Makro. Chemie I23/124 (1984), pages 437 et seq).
During the hardening of coatings containing such binders, the volatile neutralizing agents are eliminated again so that the films become insoluble in water.
Where the quality of the coatings has to meet certain requirements, for example where the coatings are required to show high solvent resistance, the coatings are normally hardened at elevated temperature using crosslinking resins. Known crosslinking resins for this purpose are, for example, etherified melamine resins or even blocked polyisocyanates (cf. for example Wagner/Sarx, Lack-Kunstharze, Carl Hanser Verlag Munchen 1971, pages 71 et seq and pages 161 et seq).
One feature common to all these crosslinking resins is that low molecular weight volatile cleavage products which are not incorporated in the coatings are formed during the crosslinking reactions (Journal of Paint Technology 46, no. 593 (1974), pages 46 et seq; Progress in Org. Coatings 12, (1984), pages 309 et seq).